As generally known in the art, as a steering apparatus of an automobile, a hydraulic power steering apparatus using hydraulic pressure of a hydraulic pump has been used. However, an electronic steering apparatus using a motor has been widely used since 1990s.
As compared to the existing hydraulic steering apparatus in which a hydraulic pump of a power source supplying auxiliary steering power is driven by an engine so that it continuously consumes the energy irrespective of the rotation of a steering wheel, the electronic steering apparatus is configured such that upon the occurrence of a steering torque by the rotation of the steering wheel, a motor supplies the auxiliary steering power proportional to the steering torque generated. Thus, the use of the electronic steering apparatus can improve the energy efficiency relative to the use of the hydraulic steering apparatus.
FIG. 1 is a constructional view of an electronic steering apparatus according to the prior art, and FIG. 2 is a partial sectional view of the electronic steering apparatus according to the prior art.
As shown in FIGS. 1 and 2, the electronic steering apparatus generally includes a steering system 100 extending from a steering wheel 101 to both wheels 108, and an auxiliary power mechanism 120 supplying auxiliary power to the steering system 100.
The steering system 100 includes a steering shaft 102 in which an upper portion thereof is connected to the steering wheel 101 to rotate together with the same, and a lower portion thereof is connected to a pinion axis 104 by means of a pair of universal joints 103. In addition, the pinion axis 104 is connected to a rack bar 109 via a rack-pinion mechanism 105, and the rack bar 109 is connected, at both ends, to wheels 108 through a tie rod 106 and a knuckle arm 107.
The rack-pinion mechanism 105 is configured such that a pinion gear 111 provided on the lower portion of the pinion shaft 104 and a rack gear 112 provided on one side of the circumference of the rack bar 109 are engaged with each other, so that a rotational motion of the pinion shaft 104 is converted into a linear motion of the rack bar 109 through the rack-pinion mechanism 105. Thus, when a driver manipulates the steering wheel 101, the pinion shaft 104 is rotated, allowing the rack bar 109 to linearly move in an axial direction, causing the wheels 108 to be steered through the tie rod 106 and the knuckle arm 107.
The auxiliary power mechanism 120 includes a torque sensor 121 that detects a steering torque applied to the steering wheel 101 by a driver, and outputs an electric signal proportional to the detected steering torque, an electronic control unit (ECU) 123 that generates a control signal on the basis of the electric signal transmitted from the torque sensor 121, a motor 130 that generates auxiliary steering power on the basis of the control signal transmitted from the ECU 123, and a reduction device 140 having a worm 201 and a worm wheel 203 for transmitting the auxiliary steering power generated from the motor 130 to the steering shaft 102.
The reduction device 140 includes a worm axis 210 having the worm 201 at one side of the circumference thereof, and rotatably supported, at both ends, by bearings 205 and 206, wherein the worm 201 is configured to be engaged with the worm wheel 203 provided on a specified position of the circumference of the steering shaft 102, and the worm axis 210 is driven by the motor 130.
Accordingly, in the electronic steering apparatus, the steering torque generated by the rotation of the steering wheel 101 is transmitted to the rack bar 109 via the rack-pinion mechanism 105, and the auxiliary steering power generated from the motor 130 based on the steering torque generated is transmitted to the steering shaft 102 by the reduction device 140. That is, the steering torque generated from the steering system 100 and the auxiliary steering power generated from the motor 130 are combined together, allowing the rack bar 109 to move in an axial direction.
However, in the reduction device according to the prior art, the continuous steering by the driving of an automobile results in wearing in the teeth of the worm 201 and the worm wheel 203 as time goes by. In addition, since the most of the worm wheel 203 is made of synthetic resin, the worm wheel 203 is often shrunk during the cold winter season.
In such a case where the teeth of the worm 201 and the worm wheel 203 are worn out, or the worm wheel 203 is shrunk, a gap occurs between the teeth of the worm 201 and the worm wheel 203, causing a problematic backlash on a teeth engagement between the worm 201 and the worm wheel 203.
Further, the reduction device according to the prior art has a problem in that a reverse input occurs due to kick-back or the like, so that upon applying an excessive torque to the reduction device, noise is generated from gaps between the worm axis and the bearings provided at both ends thereof.
In order to solve these problems, according to the prior art, two resilient bodies are inserted into the worm axis so as to apply resilient force in a radial direction and an axial direction of the worm axis, which however causes a problem in that the number of the parts increases, and the working process becomes prolonged.